Task chairs, commonly found in office and other work environments, typically include an arrangement to enable the sitter to adjust his posture between upright and reclined positions. It has been observed, reportedly, that one sitting at a desk or other work space may shift posture or position within the chair as often as approximately once per minute. Desirably, such chairs should be comfortable throughout the range of user-shifted positions. Movement through the range of chair movement should require little effort. The chair should present even resistance to the user's movement and should avoid a sense of instability. The resistance should be low and as close to uniform, as sensed by the user, as possible. The chair, desirably, should require no effort by the user to maintain the chair in a selected reclined position. This quality, referred to as “dwell” may be considered as the ability of the chair to maintain a balanced position at any attitude within the recline range of the chair.
Task chairs having a reclining feature require a number of considerations in order to facilitate comfort, reduce stress and minimize user effort when changing positions. Reclinable chairs may take any of a number of general configurations, including those in which the entire chair, including the seat and back, tilt back, as well as those in which the seat back and seat of the chair are mounted to a frame so that they can move relative to each other.
A common feature of reclinable or tiltable chairs is a spring mechanism to bias the chair components toward an upright position. These mechanisms typically include powerful springs to generate sufficient force to reduce the effort of the sitter when shifting between reclined and upright positions. The spring mechanisms are designed to apply a progressively increasing resistance force as the user reclines in order to counteract the increase in load supported by the back of the chair. The spring force stored during recline serves to assist the user when returning to an upright position. The use of such spring mechanisms generally results in variation in the force necessary to shift the degree of incline at various portions of the range of movement of the chair resulting in an uneven resistance and feeling of instability. In those chairs having separately movable seat and back portions, complex linkages and pivots may be used in an effort to optimize the motion of the chair components between upright and reclining positions that will be comfortable and will provide desired degree of support for the user throughout the range of motion.
Chairs having such spring and linkage mechanisms typically are complex and difficult to design and assemble. Additionally, they tend to be costly. The spring and linkage mechanisms for such chairs typically are among the most expensive of the chair components.
Also among the difficulties with those reclinable or tiltable chairs having a spring mechanism to bias the chair in the upright position is that the force applied by the spring must be adjusted or tuned for the particular user. Larger, heavier users will require an adjustment to increase the force of the spring while smaller, lighter users will require adjustment to a reduced spring force. This may be problematic in shared use environments, such as conference rooms, where a particular chair may be used by different users at different times or where the user may not be familiar with the adjustment controls of the chair. Even where a chair is dedicated for a single user, the adjustment and tuning mechanisms may not be understood and the user may be unable to or may find it difficult to adjust the chair.
Such chairs may be provided with some form of lumbar support intended to relieve spinal stress and back fatigue by bearing against the lumbar region of the back, particularly when the user is sitting in an upright position in which the weight of the user's torso is on the spine and pelvis. When the user is in a reclined position, the weight of the torso is distributed more evenly and over a broad area so that the force and pressure on the spine and the back muscles is lessened. Consequently, in a reclined configuration, the presence of enhanced lumbar support is not as important as when the sitter is in an upright position. Indeed, a pronounced lumbar support in a seat back may be found to be uncomfortable when the seat back is reclined. In those chairs in which a lumbar support is adjustable, it may be necessary for the user to manually adjust the configuration of the lumbar support when shifting between upright and reclined positions.